Small paucispeciflc banks constructed by the massive scleractinian Siderasirea occur along the northern margins of hermatypic coral distribution during the Miocene and Pliocene epochs. Quantitative studies of environmental variation in one bank-builder, S. mendenhaltt, from sandstones north of the Gulf of California show that distinctively thin, closely spaced synapticulae form in turbid, nearshore habitats in the same manner as in modern S. siderea from Jamaica. Analysis of variation between Siderasirea species suggests that, like these nearshore populations, framework-building species have comparatively large corallite diameters; thin septa, columellae, and walls; and numerous synapticular rings. These results imply that skeletal configurations of Tertiary bank-building Siderastrea may have been uniquely adapted for rapid colony growth in turbid, protected environments with abundant suspended organic material.